Amato DeLuca, who represents Tsarnaev’s widow, Katherine Russell, and her family, said Anna and Rebecca Russell testified at the federal courthouse in Boston. Their parents, Judith and Warren Russell, testified before the grand jury in September, but Katherine hasn’t been called.

A spokeswoman for the U.S. attorney’s office would not confirm that the Russell sisters had testified. She did not respond to questions about why they were called or whether Katherine Russell is being investigated for anything having to do with the April 15 bombing.

Three people were killed and 260 people were injured when two pressure-cooker bombs went off at the finish line of the Boston Marathon. Tsarnaev was later killed in a shootout with police. His brother, Dzhokhar, was indicted on 30 counts in June and faces the possibility of the death penalty. Three of his friends were also indicted for allegedly lying to investigators or trying to cover up his role after the bombings.

DeLuca told the AP that the sisters had visited Katherine on occasion in Cambridge and knew the Tsarnaevs but had no suspicions about them. He said he believed prosecutors are calling everyone who has any possible connection to the brothers.

“I think what they are doing is what you expect them to do. Look at everyone and talk to everyone who has any possible information, and see what comes of it,” he said. “Because of the nature of it, they’re bringing in everyone.”

Russell hasn’t been charged with any wrongdoing and has been questioned several times by federal investigators.

She, her husband and their 3-year-old daughter had been sharing a cramped apartment in Cambridge before and after the bombings. She and the girl moved to her parents’ home in North Kingstown, R.I., after her husband was killed.